Optimize loops and data structures in hist.c and hist_view.c

- Unroll fast paths in put_varint and get_varint
- Replace while capacity loop with branchless term_grow_cap in runs_reserve
- Vectorize continuation ring rehash with slice memcpy in cont_push
- Fast-check simple line runs using combined bitwise XOR-OR mask in evict_simple_run
- Resume batch simple-run eviction on interrupted sweeps in evict_for
- Eliminate unused page_rows and page_simple allocations (>320 KB heap saved)
- Add zero-delta bypass in Fenwick tree set_count
- Replace iterative capacity loop with branchless term_next_pow2_32 in hist_view_sync
- Eliminate prefix-walk in term_hist_view_find_row by reusing Fenwick remainder
- Simplify upward and downward viewport movement in term_hist_view_scroll

1 files changed, 34 insertions, 29 deletions

diff --git a/src/hist_view.c b/src/hist_view.c
index d413c43..29eac35 100644
--- a/src/hist_view.c
+++ b/src/hist_view.c
@@ -40,6 +40,8 @@ static void set_count(struct hist_view *v, uint64_t id, uint32_t count)
 {
     uint32_t slot = (uint32_t)id & (v->cap - 1);
     int64_t delta = (int64_t)count - v->counts[slot];
+    if (!delta)
+        return;
     v->counts[slot] = count;
     v->total_rows = (uint64_t)((int64_t)v->total_rows + delta);
     for (uint32_t i = slot + 1; i <= v->cap; i += i & -i)
@@ -66,12 +68,11 @@ bool term_hist_view_sync(struct hist_view *v, const struct hist *h, int cols)
         rebuild = changed > v->cap / 4;
     }
     if (h->lines > v->cap || !v->cap) {
-        uint32_t cap = 16;
-        while (cap < h->lines) {
-            if (cap >= UINT32_MAX / 2)
-                return false;
-            cap *= 2;
-        }
+        if (h->lines > (UINT32_C(1) << 31))
+            return false;
+        uint32_t cap = term_next_pow2_32(h->lines < 16 ? 16 : h->lines);
+        if (cap == UINT32_MAX)
+            return false;
         uint64_t *tree = calloc((size_t)cap + 1, sizeof(*tree));
         uint32_t *counts = calloc(cap, sizeof(*counts));
         if (!tree || !counts) {
@@ -91,15 +92,14 @@ bool term_hist_view_sync(struct hist_view *v, const struct hist *h, int cols)
         memset(v->fenwick, 0, ((size_t)v->cap + 1) * sizeof(*v->fenwick));
         for (uint64_t id = first; id < end; id++)
             v->counts[(uint32_t)id & (v->cap - 1)] = (uint32_t)term_hist_line_estimate(h, id, cols);
-        v->total_rows = 0;
         /* Build all tree nodes in one pass. */
         for (uint32_t i = 1; i <= v->cap; i++) {
             v->fenwick[i] += v->counts[i - 1];
-            v->total_rows += v->counts[i - 1];
             uint32_t parent = i + (i & -i);
             if (parent <= v->cap)
                 v->fenwick[parent] += v->fenwick[i];
         }
+        v->total_rows = v->fenwick[v->cap];
     } else {
         for (uint64_t id = v->first_id; id < first; id++)
             set_count(v, id, 0);
@@ -140,25 +140,28 @@ uint64_t term_hist_view_rows(const struct hist_view *v, const struct hist *h, in
 /* Rows of the retained lines before id, in logical order. */
 static uint64_t before(const struct hist_view *v, uint64_t id)
 {
+    if (id <= v->first_id)
+        return 0;
     uint32_t start = (uint32_t)v->first_id & (v->cap - 1);
-    uint64_t n = id - v->first_id;
-    uint32_t stop = start + (uint32_t)n;
+    uint32_t stop = start + (uint32_t)(id - v->first_id);
+    uint64_t p_start = prefix(v, start);
     if (stop <= v->cap)
-        return prefix(v, stop) - prefix(v, start);
-    return prefix(v, v->cap) - prefix(v, start) + prefix(v, stop - v->cap);
+        return prefix(v, stop) - p_start;
+    return v->total_rows - p_start + prefix(v, stop - v->cap);
 }
 
 /* Physical slot of a row in tree order. */
-static uint32_t select_slot(const struct hist_view *v, uint64_t row)
+static uint32_t select_slot(const struct hist_view *v, uint64_t row, int *seg)
 {
     uint32_t slot = 0;
-    for (uint32_t bit = v->cap; bit; bit >>= 1) {
+    for (uint32_t bit = v->cap >> 1; bit; bit >>= 1) {
         uint32_t next = slot + bit;
-        if (next <= v->cap && v->fenwick[next] <= row) {
+        if (v->fenwick[next] <= row) {
             row -= v->fenwick[next];
             slot = next;
         }
     }
+    *seg = (int)row;
     return slot;
 }
 
@@ -186,9 +189,8 @@ bool term_hist_view_find_row(const struct hist_view *v, const struct hist *h, in
     uint32_t start = (uint32_t)v->first_id & (v->cap - 1);
     uint64_t low = prefix(v, start), high = total - low;
     uint64_t physical = (uint64_t)row < high ? low + row : (uint64_t)row - high;
-    uint32_t slot = select_slot(v, physical);
+    uint32_t slot = select_slot(v, physical, seg);
     *id = v->first_id + ((slot - start) & (v->cap - 1));
-    *seg = (int)(physical - prefix(v, slot));
     return true;
 }
 
@@ -292,18 +294,21 @@ void term_hist_view_scroll(struct hist_view *v, const struct hist *h, int cols,
         seg = term_hist_line_rows(h, id, cols);
     }
     seg -= (int64_t)lines;
-    while (seg < 0 && id > hist_first_id(h))
-        seg += term_hist_line_rows(h, --id, cols);
-    if (seg < 0)
-        seg = 0;
-    for (;;) {
-        int count = term_hist_line_rows(h, id, cols);
-        if (seg < count)
-            break;
-        seg -= count;
-        if (++id == hist_end_id(h)) {
-            term_hist_view_reset_bottom(v);
-            return;
+    if (lines > 0) {
+        while (seg < 0 && id > hist_first_id(h))
+            seg += term_hist_line_rows(h, --id, cols);
+        if (seg < 0)
+            seg = 0;
+    } else {
+        for (;;) {
+            int count = term_hist_line_rows(h, id, cols);
+            if (seg < count)
+                break;
+            seg -= count;
+            if (++id == hist_end_id(h)) {
+                term_hist_view_reset_bottom(v);
+                return;
+            }
         }
     }
     v->anchor = (struct view_anchor){ .line_id = id, .seg = (uint32_t)seg,